The invention relates to a device for processing of printing defects detected in a printing machine delivering a printed product for the packaging industry starting from a support such as sheets or continuous webs of paper, cardboard or another flexible material such as polyethylene.
The invention mainly relates to a decision aid for inter alia displaying, e.g. in schematic, tabular or image form, an entire support such as a web with all the faults which spoil it and have previously been detected by a conventional device. By means of various virtual filters, the decision aid can display a number of cases of patterns or designs representing the quality level of the web and can in each case number and locate all portions of web which are covered with excessively marked defects and must be removed, even before irremediably cutting out the defects and ejecting them from the web.
Flexible packaging, made specifically from web material, is produced in various successive phases during which the reels must be repeatedly unwound and wound in order to print the web and the pack the products for which the packaging is intended.
A first step begins with printing the web, starting from a virgin reel having a width which can usually contain a number of generally identical packaging imprints. The number of imprints thus disposed side by side across the width of the web defines the number of tracks in the web. Once printed, the web is dried and examined by a device for detecting, recognising and recording all the kinds of printing defects which it may prevent. These defects are located in a Cartesian system and stored by the detection and locating device, which registers their position with respect to an origin in the longitudinal direction and with respect to the various tracks occupied in the transverse direction. Some devices can detect xe2x80x9cnascentxe2x80x9d defects, resulting generally from wear or a drift of one component of the rotary press and inevitably increasing as the printing proceeds. Any defect found will require intervention by the machine operator, who will mark the approximate place where the fault was detected by placing a sticker (cardboard tab) on the web so that when the web is rewound, the sticker projects slightly from its edge and is easily detectable. Intervention may alternatively be via an automatic labelling machine. If necessary, the machine operator may even have to stop printing in order to eliminate the possible cause of a nascent defect before it becomes unacceptable. After being inspected, the printed web is rewound in the case of machines which deliver a product in reels, as opposed to products presented in sheet form.
The second step in the conventional process consists in taking the printed reel and cutting it longitudinally to form a number of small reels equal to the number of tracks on the web. To this end, the printed web is again progressively unrolled and inserted into a rotary cutter which divides it longitudinally along a line defined by the boundaries of the tracks therein. During the web unwinding phase, the operator must attentively look out for the approach of all the stickers previously attached to the web. On arrival of each sticker the web must be stopped and the operator will have to find the detected fault and see where it begins and where it ends before eliminating it by two transverse cuts in the tracks in question. After the defective portion has been removed, the appropriate ends of the tracks are stuck together, e.g. with sticky tape. The tracks are then all simultaneously re-wound before being delivered in the form of independent reels to the customer, who will pack his products by again unrolling each small reel in a third and final step.
The invention is of use mainly in the second step, before the conversion of the printed reel begins. Devices for detecting printing errors are already known, such as those previously mentioned and illustrated in patents EP 452 769 and EP 554 811, where cameras and monitor screens are used to display faults appearing in a web or on material in sheet form during printing.
The printed webs can either serve as base material for machines producing packaging in the form of sheets, or can be re-worked and re-stored in the form of smaller reels for packing products in packaging taken off rolls. The first kind of products are very easy to manipulate, more particularly as regards removing and ejecting all defective articles from the production line, though of course it is not so easy to perform this operation on products stored in the form of continuous webs. In the case where the packaging end product is a continuous web stored on a reel, it is difficult and much more expensive to eliminate all parts of the web which have been judged defective. During the first step, elimination of such portions will necessitate a complete stoppage of the printing machine, which will seriously affect the production rate and may cause other problems in subsequent printing during the always difficult phase of restarting the rotary press. Elimination of the defective portions during the second step will result in the same problems, in this case with the rotary cutter. This machine, however, has the advantage of being simpler in construction and less fragile and of not presenting any special risk to the web when the web has to follow repeated successive stops and starts.
The number of joins in the final reel, however, will largely affect the estimate of its quality and of course consequently affect its selling price. For technical reasons which can easily be checked, it is found that joins in webs regularly pose problems in the product-packing machines which constitute the third step in the use of these reels. In view of these problems, many customers make it a general rule that these reels should not contain more than two or three joins, notwithstanding any residual printing faults which they may contain.
No device known hitherto can display the state of the web in its entirety together with its defects in order to process them in the a priori limitless cases which may occur. Each case represents a certain modulation in the degree of tolerance of these defects, so as to optimise production and obtain the best possible compromise between the maximum number of joins permitted by the customer and the number of residual defects which can still be considered as admissible.
The object of the invention therefore is to provide a tool for overall evaluation of the quality of printing of the web and for defining, using various possible scenarios and before irremediable cutting, all those portions which it is considered appropriate to reject as a priority, starting from the maximum number of web joins permitted by the customer.
This object is achieved by a device comprised of a defect detection station including an imaging device positioned to inspect the printed product as it moves along a travel path and a first data processing unit which is programmed to generate data representing individual printing defects in the printed product from signals generated by the imaging device, data representing the location of the printing defects in terms of a Cartesian reference system applying to the support layer and to record the generated printing defect data in a database that is capable of simultaneously storing data relating to all of the detected printing defects in the printed product. The device is further comprised of a defect processing station including a second data processing unit programmed to be responsive to data representing all of the defects in the printed product stored in the data base and to at least one quality-defining criterion to evaluate the quality of overall printing of the printed product and to generate finishing instructions for selecting those defective portions of the printed product to be removed to obtain a desired final quality level for the printed product and further includes a device that executes the finishing instructions generated by the second data processing unit.